This invention relates generally to a composition and method for insulating roadways to prevent icing and, more particularly, to a method for incorporating foam plastic pellets into the final surface layer, or wearing course, of a paved road.
It is well known that roads, bridges, expressways, and overpasses can ice over in periods of low temperature, resulting in unsafe driving conditions. Bridges and overpasses are particularly susceptible to this problem because they have a higher content of cold-conducting metal in their structures and more of their surface area is exposed to wind and low temperatures than that of typical roadways. The tendency of bridges and overpasses to ice over earlier than the approach pavement can result in severe accidents when unsuspecting motorists encounter an iced-over bridge after traveling on a relatively safe roadway.
Numerous methods have been employed in an attempt to reduce the danger created by this phenomenon. Some methods, such as the application of salt or sand to a roadway, are implemented shortly before or after the structure freezes in an attempt to melt the ice that forms, or to provide better traction for vehicles driving on the ice. The application of sand and deicing materials, such as salt, typically transpires after icing has occurred, which is often too late for the first motorists to drive on the roadway. In addition, the necessity of repeated applications and the corrosive effect many of these materials have on the road surface result in high maintenance costs. Furthermore, these materials can be harmful to drivers and their vehicles. The materials often cause the formation of rust on vehicles, reducing their value, and the presence of loose debris on the roadway is dangerous to pedestrians and passengers, as well as harmful to the vehicles themselves.
Other attempts at a solution focus on prevention through construction of a roadway less susceptible to icing. For example, road builders have been known to apply thick layers of gravel or other non-frost susceptible materials as a base course prior to laying down the surface pavement. The gravel layers are designed to serve as a frost barrier. The disadvantage of this method is that thick layers of the material are required to achieve the desired effect. This results in very high material, transport, and labor costs. Furthermore, it is not always feasible to lay thick layers of gravel down on bridges and overpasses.
Builders have also been known to add a layer of high-grade insulating material, such as boards of plastic foam or cork, prior to applying the surface layer of the road. The foam insulation is superior to gravel because a thinner layer of material can provide the same insulative effect. Foam plastic—created from any suitable expanded plastic polymer, such as polystyrene, polyethylene, or polyurethane—is comprised of about 5% plastic polymer and 95% air. Because air is an excellent insulator, a structure containing a sufficient amount of foam plastic will be less likely to freeze. Plastic foam's quality as an insulator is well known and can be seen in coffee cups, coolers, packaging materials, and wall insulation. However, when boards of plastic foam or other high-grade insulating material are used to form an insulative sub-layer, the material is fragile and difficult to work with. Typically, an additional layer of sand must be applied on top of the insulation material prior to the use of heavy road construction equipment or the fragile material will be crushed. The need to apply an additional layer of sand as well as the difficulty inherent in transporting and installing such lightweight and fragile material make this an undesirable method.
A third method of road construction disclosed in the prior art involves the use of an insulating sub-layer comprised of foam plastic particles dispersed throughout cement. According to this method, an additional layer of traditional asphalt or concrete is applied on top of the insulating layer to serve as the wearing course. This method has the disadvantage of requiring the application of a final surface layer of concrete on top of the insulating layer of concrete. This leads to increased labor costs because road builders must create at least two different concrete mixtures and are required to apply multiple layers.
While previous methods for insulating roadways have included layers of insulating material below the surface pavement, none have disclosed incorporating insulation material into the wearing course of a finished roadway. This is likely due to concerns about the insulating material's effect on the strength and durability of the surface pavement. However, in addition to reducing the likelihood of icing on a roadway, incorporating foam plastic into a road's wearing course rather than a sub-layer provides numerous benefits. One benefit would be lower labor costs. Because the insulating layer is the wearing course, road builders are not required to mix and spread more than one type of concrete or asphalt. A second benefit is the low cost of foam plastic itself. Foam typically costs less than the same volume of aggregate used in traditional roadways. Other benefits can be expected to arise from plastic foam's unique characteristics. For example, it is likely that a wearing course containing foam plastic will exhibit less road noise than a typical pavement and will be less impacted by environmental factors, such as extreme heat.
What is needed, therefore, is a composition and a method, which is not overly expensive or burdensome, that reduces roadway icing by incorporating insulation material into a pavement's wearing course.